Can you write part of a library in rust (pyo3) but the rest in python?

I want to write part of a python module in rust (with PYo3) but also partly in python, so something like…

src/utils.rs:

use pyo3::prelude::*;

#[pyfunction]
fn sum_as_string(a: usize, b: usize) -> PyResult<String> {
    Ok((a + b).to_string())
}

#[pymodule]
fn nvm(_py: Python, m: &PyModule) -> PyResult<()> {
    m.add_function(wrap_pyfunction!(sum_as_string, m)?)?;
    Ok(())
}

src/main.py:

from .utils import sum_as_string

...

Mostly just curious if this is possible with pyo3 or if I have to write everything in rust, cuz I’ve seen something like this done with C/Cython (example).